Synchronizing system for beam-indexing color-television display



Aug. 23, 1960 B. D. LOUGHLIN SYNCHRONIZNG SYSTEM FOR BEAM-INDEXING COLOR-TELEVISION DISPLAY Filed May 10, 1955 2 Sheets-Sheet 1 United States t. arent SYNCHRNIZING SYSTEM FR BEAM-WERKING CLR-EELEVISN DlSPLAY Bernard D. Loughlin, Lynbreolr, NX., assigner to Hazeltine Research, lne., Chicago, lll., a corporation f illinois Filed May l0, S1955, Ser. No. 507,248

S Claims. (Cl. 17d-5.4)

This invention relates to synchronizing systems for color-television receivers and, more particularly, to such systems of the type which synchronizes the color element scanning of a color-image-reproducing apparatus and the color repetition of picture signals applied thereto. This type of system has particular utility in a color-television receiver employing a cathode-ray image reproducer in which a cathode-ray beam sequentially scans primary color elements to reproduce a composite image and in which there is developed an indexing signal representative of the scanning frequency and phase of given color elements by the cathode-ray beam. For convenience, such a cathode-ray image reproducer will be referred to herein'ifter as a reproducer of the beam-indexing type.

Some prior cathode-ray image reproducers ofthe beamindexing type have employed cathode-ray tubes having phosphor screens comprising red, green, and blue lightemissive phosphor stripes disposed in repetitive succession normal to line scan. The color-repetition frequency of the picture signals applied to the cathode-ray tube, that is, the frequency of the chrominance components, is synchronized with the color element scanning frequency. For example, the red color elements may be scanned at a 7 megacycle rate, more or less. The same is true of the blue and green elements. Accordingly, the red, green, and blue color-repetition frequency of the picture signals applied to the reproducer should be 7 megacycles in synchronism with the scanning of corresponding color elements.

Due to nonuniformity of color element scanning caused, for example, by nonuniform distribution of phosphor stripes on the cathode-ray tube screen or by nonlinearities of the line scan, the color element scanning frequency and phase vary across the image raster. Accordingly, in prior reproducers of ythe beam-indexing type, an indexing signal has been developed at suitable indexing electrodes to synchronize the frequency and phase of the picture signals applied to the cathode-ray tube and the color element scanning frequency.

Moreover, because of the low amplitude of the indexing signal, high-gain circuits are employed to translate the indexing signal of varying frequency from the display screen to the electron gun of the cathode-ray tube to control the frequency of picture signals or to the linescan generator to control the frequency of color element scanning. These high-gain circuits inherently cause phase-shift variations in the translation of the indexing signal corresponding to its frequency variations. ln other Words, these high-gain indexing-signal translating circuits inherently have an over-all phase-frequency characteristic of positive phase slope. As is well known, a signal-translating circuit of positive phase slope causes a delay, known as envelope delay, in the translation of the modulation components of the translated signal. Such delay in the translation of modulation components representing the frequency variations of the indexing signal from, for example, the cathode-ray tube display screen .if fice Patented ug. Z3, 1960 to the electron gun results in color distortion of the reproduced image.

Also, changes of phase shift in the translation of the indexing signal corresponding to its frequency changes and due to a phase slope other Ithan zero of the phasefrequency characteristic cause a color distortion of the reproduced image independent of envelope delay. This color distortion is due tothe fact that as the instantaneous frequency of the indexing signal changes, the indexing signal is translated with a different phase shift from the display screen to the electron gun and hence causes a static color distortion even if the color element scanning frequency remains the same for a long enough period to allow the frequency of the indexing signal at the electron gun to be the same as the scanning frequency at the display screen.

It is an object of the present invention, therefore, to provide a new and improved synchronizing system for a color-television receiver which avoids one or more of the above-mentioned disadvantages and limitations of prior such systems.

It is another object of the invention to provide a new and improved synchronizing system for a color-television receiver employing a cathode-ray image reproducer of the beam-indexing type in which color distortion of the reproduced image is minimized.

It is another object of the invention to provide a new and improved synchronizing system for a color-television receiver employing a cathode-ray image reproducer of the beam-indexing type in which color distortion due to delay in the control of the frequency and phase of the picture signals at the color elements is minimized.

lt is another object of the invention to provide a new and improved synchronizing system for a color-television receiver employing a cathode-ray image reproducer of the beam-indexing type in which color distortion due to changes of phase shift in the translation of the indexing signal is minimized.

in accordance with a particular form of the invention, in a color-television receiver including a cathoderay image reproducer in which a cathode-ray beam having a predetermined line scan frequency sequentially scans primary color elements to reproduce a composite image and having color element scanning variations essentially repetitive at line scan frequency and including indexing means for developing an indexing signal representative of the scanning of given color elements by the cathode-ray beam, a system for synchronizing the scanning and the color repetition of picture signals applied to the reproducer comprises signal-translating means responsive to the indexing signal for controlling the color repetition of the picture signals as eective at the color elements but including circuit means inherently introducing into the indexing signal a phase shift which varies in accordance with the instantaneous frequency of the indexing signal and which delays the control of the color repetition of the picture signals accordingly. The syetem also includes circuit means responsive to the indexing signal for developing a control signal repetitive at line-scan frequency and representative of the frequency variations of the indexing signal and includes a low-pass iilter network coupled to the circuit means for translating the control signal with a phase advance at least at fundamental line-scan frequency. Finally, the system includes circuit means responsive to the advance control signal for maintaining the total elective phase shift of the indexing signal in its effective translation from the indexing means to the color elements at approximately zero value to minimize the delay of the control, thereby minimizing color distortion of the reproduced image.

For a better understanding of the present invention,

. it tu. 47K. it together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed yout in` theappended claim/s.. 1-, s,

Referring to the drawings: 'Y Y 'Fg; 1 is ajschematie diagram ofa colY r'V-televisionrreceiver'includinga synchronizing system constructed in' accordance with the invention; Y v

Fig. 2. is a detailed circuit diagram-representing an equivalent circuitof a portion of the Fig. l receiver; Y

Fig. 2a a graph Yrepresenting the phase-frequency characteristic ofthe Fig; 2circuit,vand` Y Y Fig.-3f is a schematic circuit diagram of an embodiment of the invention in modified form.

General description and operation of Fg.'/1'receyer ReferringnovvY more particularlyto jFig. V1 of the drawings, :there Yis representedV a color-television receiver including a cathode-ray image reproducer Yof conventional construction Vin,` which a'cathode-ray beam sequentially scans 'primarycolor elements to reproduce a composite image fand including indexing means Yfor developing an indexing signal representative of the scanning of given color elements by the cathode-raybeam.-V In 245 order to apply suitable picture signals to the cathode-ray' image reproducer, the receiver includes an antenna sys- ,4 for example, be a reference-signal generator ZZVcoupled to the band-pass lter 15 and to the line-scan generator 19 for gating the color burst of the signal n'om unit 15 and having an output circuit coupled to a variable phaseshift circuit 23 for varying the phase of the reference signal in a manner more fully explained subsequently.

An oscillator 28 iscoupled to input electrodes of the A cathode-rayrimage reproducer .l'for modulating the intensity of the Vcathode-ray beam thereof at a frequency of, for example, v52 megacycles Yto providera low-level indexing-signal carrier. In'this connection, the cathoderay tube of'unit 10 may be ofthe single-beam type or of Y the dual-beam type, the latter developing a separate lowintensity beam modulated by the indexing-signal carrier.

The system 17 Valso includes signal-translating means responsive to the indexing signal developed in the cathode-ray image reproducer 10 for controlling the relation of the scanning of givencolor elements and the color Iepetition'of the picture signals aseffective at the color elements but inherentlymdelaying'the control of the aforesaid relation. Forclarity of expression, the term indexing signal will be employed .to refer to a signal which carriesinformation representing the scanning of the color elements of the display screen, although this signallmay, undergo frequency conversions and also carry additional information in its translation around a tem 11,311 oiconventional constructionV toV which the following are connected in cascade: Vradio-frequency stages and detector 12 also of conventional construction for derivingvideo-frequency modulation components of the received television signal with chrominance-signal components at `approximately 3.6'megacycles; a code trans-v lator 13 of conventional construction, preferably of the type described in an articleV by applicant entitled Proc' essing of theNTSC Color Signal for One-Gun Sequential Color Displays, Proceedings of the I.R.E., January 195,4, andfalso known as a Y-toA-M converter and subcarrier modifier, for converting the video-frequency modulation components to'a so-called dot-sequential signal having 'chrominance ',componentsrat Yapproximately 3,6 mega- Vcycles and a luminance-correction component?Y and a complete circuit loop. Y

'I'.he signal-translating means includes circuit means inherently introducing into the indexing signal a. phase shift which varies in accordance with the Vfrequency of the indexing signal, for example, a relativeqphase lag which. is proportional to trerpiencyV and whichk delays control ofthe frequency of the picture signals accord-V 7 ingly. More particularly, this circuit means comprises .a high-gain indexing-signal amplifierV 24 of conventional construction tuned to -a sidefrequency of the indexingsignal carrier, for example, .megacycles,`A a modulator 25 responsive to the indexing signal, to the phase-shifted reference signal developed in theY output circuit of unit 23, andjto the output signal of the oscillator 28 forY ldeveloping a variable frequency heterodyne signal, and Ia `secondY modulator 1 6 responsive to'received picture signals translated by the bandfpass `iilter 1,5. and to the heterodyne` signalydeveloped by the modulator 2,5.,'for

pass band of, for example, 3.0-4.2 megacycles for transi quency VofapproximatelyV 7V Vmegacycles and VproperlyY synchronized with the color element scanning. The receiver also includes a suitable synchronizing-signal separator '18 `for separating the line-scanv and'iield scansynchronizing-components from the output signali ofthe detector of unit 112.; `The separator '18 applies the line-scanjandiield-scansynchronizing components to line-- scali iandjfleld-scan generators 1,9fand 20, respectively, which are connected to the reproducer 10 for controlling the 'Samling 'Operations thereof to develop an image Yrasterlvdeveloping lpicture signals, having a Vfrequency Vsynchro-` mzed with the color `element scanning lfrequency of the cathodefrray image reproducer 10. Y.

' Thepsystem 17- `also includes circuit means responsive tothe indexing signal `and coupled tothe `signal-trans-V lating means for Vadvancing theon'trol ofthe laforesaid relationY to minimize thedelayof that control, -thereby color distortions of thereproduced image.Y More particularly, this circuitV means is etfectiveto introduce a phaseshjft which varies inaccordance with the frequency of lthe indexing Asignal and which is of such magnitude and sense as to adyancefthe control Vof the frequency of the picture signalstto minimize the delay f; of that control by maintainingV the total effective phase shiftof theuindexing signal in its eifectiyeqtranslation from the indexing means Vto the color elementsfof unit 10 at approximately zero value, In this connection, as will .be more fully explained subsequently, the frequency f j variations of the indexing/signal'are essentially repetitive Y The receiver alsoincludes a conventional sound-re comprises circuit means foi-*supplying "asubarrier ,refer-1 ence Signal srnhropizedfnithf fhQQlQr bnrstof apre: ceivedcomposite video signal. This circuitnieans may,

at line-scan frequency and,` in orden-toV the delay of the lfrequency control, `the frequency control advancing circuit meansY maintains ,approximately zero Vphase shift for modulation :components Vwhichfare harmonies of line-scan Ifrequency.

The frequency control advancingcir/cuitvr means preferably comprises A frequency-responsive circuit mean's Yfor example, -a frequency-modulation ldetectorlft responsive to the indexing signal, as represented bythe heterodynesignal output of modulator-25,1for developing Va Vcontrol signalrepetitivaat linefscanV equency andfrepresenta tive Qi the'irequency' 'variations ofthe Yindexing signal.

The frequency control advancing circuit means also includes a low-pass filter network 27 coupled to the detector 26 for .translating the control signal with a phase shift at harmonics of the line-scan frequency, which phase shift is proportional to the Iharmonic frequency. The term harmonic of line-scan frequency is meant to include fundamental line-scan Ifrequency. The filter 27 preferably comprises a multi-resonant circuit resonant slightly above harmonics of line-scan frequency for translating the control signal with a leading phase shift at least at fundamental line-scan frequency. The Variable phase-shift circuit 23, also included in the frequency control advancing circuit means, may be of conventional construction comprising, for example, `a reactance tube coupled across a resonant circuit tuned to the frequency of the reference signal. rl`he circuit 23 is coupled to the output circuit of the ylow-pass lter 27 and to the modulator 25 of the signal-translating means for introducing a phase shift which varies in accordance with the frequency of the indexing signal and which is of such magnitude and sense as to maintain the total effective phase shift at approximately zero value, thereby maintaining an over-all effective phase-frequency characteristic of zero phase slope.

Operation of Fig. l synchronizing system Considering now the operation of the Fig. .1 system .17, the cathode-ray beam of the cathode-ray image reproducer iti during each line scan sequentially scans the color elements or stripes of the cathode-ray tube and develops at a suitable indexing electrode thereof an indexing signal representative of the scanning of stripes of a given color. Due to nonuniformity of color element scanning caused, `for example, lby nonuniform distribution of phosphor stripes on the cathode-ray tube screen or by nonlinearities of line scan, the color element scauning frequency and phase vary across the image raster. This scanning frequency may, for example, be approximately 7 megacycles and ordinarily varies across each line as the line is scanned with yat most a slight variation at field-scan frequency. Accordingly, the frequency variation of the indexinC signal is essentially repetitive at ine-scan frequency.

Because of oscillator 23 which supplies a carrier signal for the indexing signal in a manner more fully described presently, the indexing signal developed at the output electrode of the reproducer -lti may have a varying frequency of, for example, approximately 45 megacycles corresponding to a side frequency of the carrier signal. This indexing signal is amplified by amplifier and applied to modulator 25 wherein it beats with the output signal of oscillator 23 having a frequency of, for example, 52 megacycles and with the reference signal from unit 23 having a frequency of approximately 3.6 megacycles to develop a heterodyne signal having a frequency of, for example, 19.6 megacycles.

The heterodyne output signal of the modulator 25 is applied to the modulator le while the picture signals and, in particular, the corrected chrominance components transrated by the band-pass filter are applied to another input circuit of the modulator 16. The signals applied to the modulator lo beat together in the modulator to develop output picture signals having a frequency of approximately 7 megacycles for application to the electron gun of the cathode-ray image reproducer iti.

Assuming for the moment the absence of circuits for advancing the control of the frequency of picture signals constructed in accordance with the invention, then, due to the inherent positive phase slope of the over-all phasefrequency characteristic of the indexing-signal amplifier 24 and modulators Z5 and i6, the modulation components representing frequency variations of the indexing signal are delayed in translation from the indexing-signal output electrode of the cathode-ray image reproducer lll to the electron gun thereof. Also, the modulation information representing frequency variations of the indexing signal is delayed in translation from the electron gun of the reproducer 10 to the display screen thereof Within the cathode-ray tube. Accordingly, the control of the frequency of the picture signals as effective at the color elements of the display screen of the reproducer 10 is inherently delayed by the indexing-signal translating circuits.

The manner in which the system 17 advances the control of the frequency of the picture signals as effective at the color elements to minimize or eliminate the delay of the control will now be considered. The 10.6 megacycle heterodyne signal representing the indexing signal and developed in the output circuit of the modulator 2S is applied by the modulator 2S to the frequency-modulation detector 25. The detector 26 derives from the signal applied thereto a control signal repetitive at line-scan frequency because of the repetitive frequency variations of the indexing signal at line-scan frequency. Because of its repetitive nature and in accordance with Fourier analysis, the output signal of the detector 26 comprises a directcurrent component, a fundamental component at line-scan frequency, and components at some harmonics of linescan frequency.

The detector 26 applies the control signal toy the lowpass lter 27 having an equivalent circuit represented diagrammatically in TEig. 2. The low-pass filter 27 includes, for example, a signal source represented by a constantcurrent generator 33. The constant-current generator is coupled across a multi-resonant circuit including a resistor 29 by-passed at line-scan frequency by a condenser 259:2 for deriving the direct-current component of the control signal, a first tuned circuit Stil for deriving the fundamental component, a second tuned circuit 31 for deriving the second harmonic component, and a third tuned circuit 32 for deriving the third harmonic component. Additional resonant circuits tuned to derive higher harmonic components of the control signal may be included in the lowpass filter if necessary for a particular application. Also, fewer resonant circuits may be utilized if desirable for a particular application. It should be understood that many 10W-pass filter circuits may be employed which have similar characteristics to the equivalent circuit of Fig. 2, for example, a ladder iilter simulating a delay line and terminated in a high impedance at both terminals.

Referring now more particularly to Fig, 2a of the drawings, there is represented the phase-frequency characteristic of the Fig. 2 circuit. The resonant frequencies of the resonant circuits '30, 3i, 32 are indicated as frequencies 1530, fab fag While the harmonic components of the control signal occur at frequencies f1, f2, f3. As represented in Fig. 2o, the resonant circuits 30, 3l, and 32 are so tuned that corresponding components of the control signal are developed across the circuits with a leading phase shift which is proportional to the harmonic frequency. In the embodiment represented, the circuits are individually tuned slightly above the harmonic frequencies. The value of the resistor 29 and the Q of the tuned circuits are so proportioned that the frequency components of the control signal are translated by the filter 27 with proper relative amplitudes to provide a desired reproduction of the input control signal.

Because the leading phase shift of each frequency component translated by the dlter 27 is proportional to the frequency of that component, the filter 27 operates during the translation of the control signal as if it has a constant.v

negative phase slope corresponding to the slope of broken line A of Fig. 2a. Accordingly, the control signal in the output circuit of the filter represents the control signal at the input circuit of the filter but leads the input signal with a `time advance proportional to the apparent negative phase slope.

The advanced control signal is eifective to control the phase of the reference signal translated by the variable phase-shift circuit 23. The variation of the phase shift of the reference signal is such that the total effective phase shiftoflthe indexingsignal developed at the output elec:

' frode of therreproducer 10 has approximately zero valueV `in its translation fro'nrth'efoutput electrode through the signal-translating'means :24, 2.5,V 16 and through the cathode-,ray tubeto the display screen as acontrol of the frequency ofthe Vpicture signals at the display screen. In this connection, it is assumed that` the chrominance signal applied te? the'rnodulator 16 corresponds in phase to the color` correspondingY to the position of the indexing stripes on jtherdisplay screen. Any variation from this condition means that the effective phase shift is computed with respect tov a reference value other than zero. The factthat the indexing signal has atotal effective phase shiftofzero Valuerin its translationlaround the circuit loop just described may be restated in terms that the overalleifective phase-frequency characteristic has zero Vphase slopefmAccordingly,'becausethe over-all phasefrequency'charaeteristic has Yzero phase slope, the indexing signal is notdelayed in its translation around the circuit loopand the frequency of the picture signals Vas effectiveratA the color stripes of the cathode-ray tube is exactly synchronous with the scanning of a Vgiven color stripe. In'A this manner, `color distortion is minimized. A Further, since the indexing signal has a total effective phase shiftrof zero value in its translation around the circuit loop, no phase shift Yis introduced which could cause staticrcolor distortion Yof the reproduced image.

i DescriptionY of Fig.Y 3V system Y.

Referring now more particularly to lFig. 3 of the drawings, there is represented a synchronizing system whichY may be utilized in the Fig. l receiver in lieu of the system 17 andY interconnected with the units of the Fig. 1 receiver las indicated in Fig. 3. The Fig. 3 system minimizescolor distortion of the lreproduced imagel caused by'delay in the translation of the modulation components of the indexing signal due to the phase slope of other thanY zero .value ofithe phase-frequency characteristic of the* indexing-signal translating means. Also, the Fig. 3 system static color distortion due to changes in phasesliift with frequency changes in the translation of the indexing signalby providing substantially all ofthe' ampliication'of the indexing signal at a 'substantially' constant average frequency regardless' of frequency variations'of`the indexing signal. The term averagefrequency? is meant to indicate a frequency averaged overY an interval substantially less than the periodof line scanY but more than the period of the indexing signal.

The system 40 includes an oscillator 41 of conventional construction'for'developing an output signalhaving Va frequency,V for example its average frequency, differing from that ofthe'indexing signal by a substantiallyconstant'value. Y*The output circuit of the oscillator 41 is coupled to rst circuit means comprising a modulator 42 of conventional constructionforderiving a signal Vhaving -a frequency which tends'tofvar'y, that is, having, Yfor example; a substantially constant average frequency but havingphase variations. f

. Theoutput circuit ofthe modulator 42Ais Vcoupled Y through a' high-gain amplifier `43 of conventional construction to second circuitY means comprising, for example,

' a phase detector 44fof conventional construction for deriving a repetitive control signal representative of angularlvelocity,variations of the input signal to the phase detectorrwith respectto Va reference signal applied thereto by a Yreference-signal generator .60 similar to gen-V jThe output circuit of the Aphasev detector 44 is'coupled through a'loW-pass filter 45 which may be of similarY construction to theloW-pa'ss iilt'er27 of the Fig. l embodiment` for translating the control signal with a phase shiftV atleast Vatfunda'rnental line-scan YfrequencyY and preferably at"otheriharmonics of`line-scan frequency,Y Which phasershiftris proportionalzto thehar'monic frequency-for maintaining lat approximately Yzero value the total elfecconventional construction responsive to the control signal for-maintaining the average frequency of the oscillator 41V at a substantially constant difference from that of the indexingV signal.

f The Vsystem .40 also includes circuit means for translating the* picture signals and responsive to the output signal of the oscillator `41 for controlling the frequency of the picture signals, thereby minimizing color distortion of the reproduced image. More particularly, this circuit means comprises, for'example, modulators 4S, 49 of conventional construction.'V The modulator 48 is responsive to the output signal of the'oscillator 41 and to the output signal of an oscillator 50 which' may be of similar construction to the oscillator 28 of the Fig. l embodiment while-the modulator 49 is responsive to the output signal ofthe modulatorf48 and to the picture signals supplied 4by the unit 15 'for deriving picture signals having a color-repetition frequency 'synchronized with the color element scanning frequency of Vthe cathode-ray image reproducer 10 of Fig. 1. Y 1

. Operationof Fig. 3 system Y e Considering now the operation of the Fig. 3 system 4l), while.. the color element scanning frequency of the cathode-rayimage reproducer 10 of Fig. l varies in the neighborhood of, for example, 7 megacycles, the unit 10 applies' an indexing signal to the modulator 42. having a corresponding lh'equency variation repetitive at line-scan frequency. The indexing signal applied to the modulator 42 Vmay have'a varying frequency of approximately 45 megacycles corresponding-toa side frequency Vof the cartier signal supplied to the unitltl by the oscillator 50.

,.The oscillator 41, which has its average frequency maintained at a substantiallyconstant difference from that of the .indexing signal applied to the modulator 42 in a manner presently tobe described, supplies to the modulator 42a heterodyne signal having a frequency of, for ex- Vthe substantially-constant--average frequencyA of, yfor example,3.6 .rnegacyclesl but having phasevariations. This signalistranslated lthroughV high-gain amplifierY 43 for amplilioationand application to phase detector 44.

The reference-signal generator 60 supplies to theY phase detector 44 a subcarrier reference signal synchronized with the color burst of the received video signal.r The phase detectorl44derives from'the indexing signal and the reference. signal a control signal representative of the phase variations. of the indexingsignal Ywith respect to the referencesignal.. This control signal istranslated by the low-pass filter `45 in a manner similar to the translation of the control signal derived by detector 26 of the Fig. 1 embodiment. Accordingly, the filter 45 elfectively ad- Vances the phase of the control-signal-output of the phase detector 44 land applies the phase advanced control signal to the reactance-tube circuit 46 which maintains the average frequency of the oscillator-'41 at -a value substantially 3.6 megacycles below the average frequency of the indexing signal. Thus, as theaverage frequency ofthe indexing signal applied to the modulator 42 varies, the instantaneous frequency of the output signal of the modulator -42 varies, causing a phase variation with respect to the output signal of the reference-signal generator which is detected by the detector 44 and utilized after suitable phase advance by lter 45 as the control signalv to vary the average frequency of theoscillator 41 accordingly.

The output signal of theVV oscillator 41 is applied to modulator 48 where it beats with the output signal of the oscillator 50 to iderive a signal having a frequency of, for example, approximately` 10.6 megacycles. This signal, in turn, beats With'the'chrominance components sup-V 9 to supply to the electron gun of the cathode-ray image reproducer lt) of Fig. 1 a signal having a frequency of, for example, approximately 7 megacycles.

Since substantially all of the amplification of the indexing-signal carrier occurs at a substantially constant frequency in the amplifier 43, the phase slope of the phase-frequency characteristic of the amplier 43 does not cause an undesirable phase shift in the indexing signal for a static-frequency change of the indexing signal in its application to the modulator 42. The modulators 4S and 49 may be designed to have a phase-frequency characteristics of approximately zero phase slope because they need not provide amplification of the indexing signal. Accordingly, the system 4ta does not cause an undesirable static phase shift in the indexing signal which would result in static color distortion due to a staticfrequency change.

Because of the phase slope of the amplier 43 which eects the translation of side-band components of the indexing signal, the amplifier 43 introduces into the indexing signal a phase shift which varies in accordance with the instantaneous frequency of the `indexing signal and which delays the modulation components of the indexing signal in their eiective translation to the color elements of the tube. For this reason, the low-pass iilter 45 is utilized to advance the control of the frequency of the oscillator 4i which compensates the delay of the modulation components around the circuit loop. The advance in the control of the frequency of the oscillator di provides an over-all effective phase-frequency characteristic for the system 4i? and the unit l@ of Pig. l having a phase slope of approximately zero value.

Prom the foregoing description, it will be apparent that a synchronizing system constructed in accordance with the invention has the important advantage that delay in the translation of the modulation components of an indexing signal representing the color element scanning is minimized or eliminated, thereby minimizing color distortion of the reproduced image. Also, static color distortion is minimized because of the ltranslation of the indexing signal from the `display screen to the electron gun of the cathode-ray tube with substantially the same effective phase shift regardless of `any static-frequency change. Moreover, it will be apparent that While systems which provide synchronization by controlling the colorrepetition frequency of picture signals have been specifically described, systems Which provide synchronization by controlling the color element scanning frequency by, for example, controlling the instantaneous sweep slope of the output signal of the line-scan generator are also Within the spirit and scope of the invention.

`While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modications may he made therein Without departing from the invention, and it is, therefore, aimed to cover all such changes and modifications as fall Within the true spirit and scope of the invention.

What is claimed is:

l. In a color-television receiver including a cathoderay image producer in Which a cathode-ray beam having a predetermined line-scan frequency sequentially scans primary color elements to reproduce a composite image and having color element scanning variations essentially repetitive at line-scan frequency and including indexing means for developing an indexing signal representative of the scanning of given color elements by the cathoderay beam, a system for synchronizing the scanning and the color repetition of picture signals applied to the reproducer comprising: signal-translating means responsive to said indexing signal for controlling the color repetition of said picture signals as effective at said color elements but including circuit means inherently introducing into said indexing signal a phase shift which varies in accordance with the instantaneous frequency of said ndexing signal and Which delays the control of said color repetition of said picture signals accordingly; circuit means responsive to said indexing signal for developing a `control signal repetitive at line-scan frequency and representative of the frequency variations of said indexing signal; a low-pass filter network coupled to said circuit means for translating said control signal with a phase advance at least at fundamental line-scan frequency; and circuit means responsive to said advanced control signal for maintaining the total effective phase shift of said indexing signal in its effective translation from the indexing means to the color elements at approximately zero value to minimize the delay of said control, thereby minimizing color distortion of the reproduced image.

2. In a color-television receiver including a cathoderay image reproducer in which a cathode-ray beam having a predetermined line-scan frequency sequentially scans primary color elements to reproduce a composite image and having color element scanning frequency variations essentially repetitive at line-scan frequency and including indexing means for developing an indexing signal representative of the scanning frequency of given color elements by the cathode-ray beam, a system for synchronizing 'the color-repetition frequency of picture signals applied to the reprcducer with the scanning frequency comprising: signal-translating means responsive to said indexing signal for controlling the color-repetition frequency of said picture signals as effective at said color elements but including circuit means inherently introducing into said indexing signal a phase shift which varies in accordance with the frequency of said indexing signal and which delays the control of said color-repetition frequency of said picture signals accordingly; frequencyresponsive circuit means responsive to said indexing signal for developing a control signal repetitive at line-scan frequency and representative of the frequency variations of said indexing signal; a low-pass filter network coupled to said frequency-responsive circuit means for translating said control signal with a leading phase shift at harmonics of line-scan frequency, which phase shift is proportional to the harmonic frequency; and variable phaseshift circuit means coupled tosaid low-pass filter net- Work Yand to said signal-translating means for introducing a phase shift which varies in accordance with the frequency of said indexing signal and which is of such magnitude and sense as to maintain the total effective phase shift at approximately zero value in the effective translation of said indexing signal from the indexing means to the color elements to minimize the delay of said control, thereby improving synchronization of said color element scanning and color-repetition frequencies and minimizing color distortion of the reproduced image.

3. In a color-television receiver including a cathoderay image reproducer in which a cathode-ray beam having a predetermined line-scan frequency sequentially scans primary color elements to reproduce a composite image 'and having color element scanning variations essentially repetitive at line-scan frequency and including indexing means for developing an indexing signal representative of the scanning of `given color elements by the cathode-ray beam, a system for synchronizing the scanning and the color repetition of picture signals applied to the reproducer comprising: signal-translating means responsive to said indexing signal for controlling the color repetition of said picture signals as effective at said color elements but including circuit means inherently introducing into said indexing signal a phase shift which varies in accordance with the instantaneous frequency of said indexing signal and which delays the control of said color repetition of said picture signals accordingly; circuit means responsive to said indexing signal for developing a control signal repetitive 'at line-scan frequency and representative of the frequency variations of said indexing signal; resonant circuit means coupled to said circuit means and resonant slightly above one or more haransiosi-.1sV

monies" 'of line-scan frequency for translating said control signal with a phaseadvance at least at fundamental linescan frequency;and Ycircuit means coupled to said resonant circuit means andV to said signal-translating means for maintaining the total elective phase shift of said indexing signal in its effective translation from the indexing means to the color elements at approximately zero value to minimize the delay of said control, thereby minimizing color distortion of the reproduced image. Y Y Y v 4. Ina color-television receiver Aincluding Y'a cathoderay image reproducer in which a'cathode-ray beam having aV predetermined line-scan frequency sequentially scans pn'maryfcolor Velements to reproduce'a' composite imagerand having color element scanning frequency variations essentially repet'itive at line-scan frequency and including indexing means for developing an indexing sigal representative of therscanning frequency of given color elements by the cathode-ray beam, a system for synchronizing the color-repetition frequency of picture signals applied to the reproducerY with the scanning frequency comprising:V signal-translating means responsive to said indexing signal for controlling the color-repetitionfrequency of'said picture `signals as effective at said color elements but including circuit means inherently introducing into said indexing signal a phase shift which varies in accordance with the frequency of said indexing signal 4 and which delaysY the control ofrsavid color-repetition frequency "of said Apicture signals accordingly; frequencyresponsive circuit means responsive to said indexing signal forI developing a control signal repetitive at linescan frequency and representative of the frequency variations of said indexing signal; a multiresonant circuitv coupled to said `frequency-responsive circuit means Yand resonant slightly above harmonics of line-scan frequencyA for translating said control signal with-a leading phase Ytroducingl a phaseshiftewhich varies in accordance Ywith the frequency. of said indexing signal and-Which is of such magnitude and sense as to maintain the total effective phase shift at approximately zero value in the effective translation of said indexing signal from the indexing means to Athe'rcolor elemeutsrto minimize theAV delay of said control, therebyY improving synchronization of said color element scanning andcolor-repetition frequencies and minimizing color distortion of the reproduced image. Y 5. InV ai color-television receiver, .asystem for synchronizing theV color-repetition equency of VVpicture signals -applied to a color-image reproducer with the color element scanning frequency thereof comprising: Va cathode-ray color-image reproducer having primary-color elements sequentially scanned by a cathode-ray beam having a predetermined line-scan frequency to 'reproduce a composite image and having colorfelement scanning frequency variations essentially repetitivefat t line-scan-frequencyand including indexing Vmeans fordeveloping Van indexing signal representativeV of the scanning frequency` of given color elementsV by the cathode-ray beam; circuit means for supplying Ya subcarrienreference Ysigna'Lsynchronized with the color burst ofv a receivedl composite vid-eo signal; a variablephase-shift circuit coupled to Ysaid supply. circuit meansforfvarying-the phase'of said ret.-Y erence signal; Vatrnodulator.'responsive to said indexing signal and tosaid phase-shifted reference signal for Vdef veloping a` variable-fre'qu'ency` heterodyne signal; a second modulator responsiveto received-.picturesignals and to. said heterodyne signalfor developing picturelsignals hav-` ing'` a. colorfrepetition 4frequency synchronized with said color element scanning frequency; Va Vfrequency-responsive detectorfforderivingV a control signal repetitive .at lines can frequency and representative Vof'frequency variations of` said ,indexing signal; a low-pass Vfilter network coupled tpV saidfrequency-responsivedetector for translating said control signal with a leading phase shift atharmonics ofline-scan frequency; which phase shift is proportional to the harmonic frequency; and said variable phase-shift circuit being responsive to said control signal for varying the phase of-said phase-shifted reference signal iniaccordance with;V the frequency of said indexingsignal to maintain the total eiective phase of said indexing signal in its Yeffective translation from said indexing means to said. color elements at approximately4 zero value to Kminimize the delay of said control, therebyimproving synchronization of said color element scanning and colorrepetition frequencies and kminimizing color distortion of theY reproduced image. Y- f Y 6. In a color-television' receiverfincluding a cathoderay image reproducer in Vwhich a cathode-ray beamsequentially'scans'primary-.color elements to .reproduce a composite image and having essentially repetitivecolor element scanning variations and including indexing means for developing an indexing signal representative of the scanning of given color elements by the `cathode-ray beam, a system for synchronizing the scanning` and the colorY repetition of picture signals Iapplied to thel reproa ducer-compris'ing: signal-translating means` responsive to said indexing ysignal for controllingtherrelation ofthe scanning of given color elementsV andthe color repetition of said picture signalsas effective at saidV color elements butlinherently tending to translate saidrindexing signal from the indexing means to the color elements with an eifectivephase shift of other thanY zero value; and oircuit ,means responsive vto repetitive variations of said indexing signaland coupledV to said signal-translating means for advancing the phase of at least the fundamental component of variations of said indexing signal to maintain the total` effective phase shift ofsaidrindexing sig- Y nal inA itsY effective translation from thegindexing means to the Ycolor elements at approximately zero value, thereyby. improving synchronization ofsaid color; element` scanning'and color repetition and color distortion of thereproduced image-1- -7..V In Aa color-telev'ision receivengfar-systemfor 'rsynchronizing lthe color-repetition frequency Yof picturemsignals appliedto a color-image Vreproducer vt/ith` ,the Acolor element` scanning frequency thereof comprising; Ya cathoderayY Vcolor-image reproducenhaving1 colQilfQlements sequentiallysoannd 'byffa QlthlQdQ-raY-hamf-ilvf ing, `a `pradeternnned Yline-scanfrequencylto,reprmiuce a composite image and Yhaving colorrelement scanningffrequency Yariations essentially Vrepetitive at ,line-scan fr equencyland including indexing means forY developing an indexing .signal Y1'apresamat-ivel of the Scanning ,frequency of given Ycolor elements bythe cathoderay beam; oscila lafarvor deyalopins' an. output signal havinsaairequency diieringrbyga substantia11y constant. value from thatOf said indexing signalirstcircuitmeans responsive Yrtv-said. indexingY Signalandto said; output signal, ofsaid `uscrilllatur.

" for deriving a Signal `having ra frestuency which tends t0 vary; lsecond ycircuit means for deriving a rpeiitiva 99H: trol signal, representative" of, angular' 4velocity variations of said' derived signal; a 10W-pass filter.j ietyvorl;` coupled tosaid second Y circuit means ,ict translating said C011- frolgsigualwitha leading phase-shiftatharmgniss `Qiliiae-` but .sisrialvof `said pscillatfit.i'fcrY ctlne, the selbireptition frequency of said Picture signalsnhsrebr i111: provinssynchronizaton Qi saisi olorlelememiS-Qannias istortionoffthe. ,reproduced imagev i,

=8. In a color-television receiver, a system for synchronizing the color-repetition frequency of picture signals applied to a color-image reproducer With the color element scanning frequency thereof comprising: a cathoderay color-image reproducer having primary color elements sequentially scanned by a cathode-ray beam having a predetermined line-scan frequency to reproduce a composite image and having color element scanning frequency variations essentially repetitive at line-scan frequency and including indexing means for developing an indexing signal representative of the scanning frequency of given color elements by the cathode-ray beam; an oscillator for developing an output signal having an average frequency differing by a substantially constant Value from that of said indexing signal; a modulator responsive to said indexing signal and to said output signal of said oscillator for deriving a signal of substantially constant average frequency but having phase variations; circuit means for supplying a subcarrier reference signal synchronized with the color burst of a received composite video signal; a phase detector responsive to said subcarrier reference signal and to said phase-varying signal for deriving a repetitive control signal representative of said phase variations; a low-pass lter network coupled to said phase detector for translating said control signal with a leading phase shift at harmonics of linescan frequency, which phase shift is proportional to the harmonic frequency for maintaining the total effective phase shift at approximately zero value for modulation components representing frequency variations of said indexing signal; frequency-control means responsive to said control signal for maintaining the average frequency of said oscillator at a substantially constant difference from that of said indexing signal; and circuit means for translating said picture signals and responsive to said output signal of said oscillator for controlling the color-repetition frequency of said picture signals, thereby improving synchronization of said color element scanning and color-repetition frequencies and minimiz- -ing color distortion of the reproduced image.

References Cited in the file of this patent UNITED STATES PATENTS 2,644,030 Moore June 30, 1953 2,671,129 Moore Mar. 2, 1954 2,674,651 Creamer Apr. 6, 1954 2,680,147 Rhodes June l, 1954 2,713,605 Bradley July 19, 1955 2,715,155 Bryan Aug. 9, 1955 2,759,042 Partn Aug. 14, 1956 2,772,324 Boothroyd Nov. 27, 1956 2,782,252 Fedde Feb. 19, 1957 2,831,052 Boothroyd Apr. 15, 1958 OTHER REFERENCES A Two-Color Direct-View Receiver for the RCA Color Television System, November 1949. (Copy in Division 16.) 

